The present invention relates to a hip joint prosthesis having an essentially cylindrical first shaft member disposed in the vicinity of its end near the joint, the first shaft member being provided with a lateral arm oriented at an angle in the direction of the end for receiving the joint ball, wherein
in its region adjacent the shaft, the dimension of the arm is substantially larger than in a direction which is tangential to the shaft; and
a second shaft member can be pushed onto the member supporting the arm so as to project beyond the first member in the direction away from the joint end.
A hip joint prosthesis of this type is disclosed in published European Patent Application No. 179,626. In this prosthesis a conical shaft extends from an arm portion which has a joint ball. The conical shaft can be extended by separate members that can be pushed onto its end. It is a drawback of this arrangement that, particularly if longer shaft lengths are involved, instabilities may develop because the overlapping of successive elements is limited to the region of a cone end portion of the conical shaft. If several extensions are employed (corresponding to known "modular prostheses"), several extension elements and their associated conical connections would be required. Additionally, the mass of the shaft is considerable, particularly for longer lengths.